A tool I use constantly in frontend development, and it works perfectly in combination with WeBuilder.

Prepros App offers compilation support for Less, Sass, Stylus, Markdown and more. Some of the other notable features in Prepros are live browser refresh, Image optimization, built-in server, multi-device testing and FTP support for deployment. It also allows the ability to create shareable configuration files which is useful when working in a team.Runs on Windows, Mac and Linux.

In case some one is looking for the same option:Just include an image folder in your project. Click on any image and you will get a dialog asking if you want to compress the image file. But be aware that the result is not great. I still prefer tinypng.com